1. Field of the Invention
The invention relates to apparatus for punching holes in tape, film and other flexible, elongate members. Such holes are required for example in magnetic-recording tape or cinematographic film strip. The holes may be apertures or alternatively recesses or depressions.
2. Description of the Prior-Art
Conventionally, film or tape which has required a longitudinal row of apertures for engagement by drive and/or guide sprockets has been provided with such apertures by a row of punches co-operating with a row of dies. Reciprocal motion is employed and the film or tape must be accurately indexed by an appropriate distance between each stroke of the punches. Aperture-forming machines operating on this principle are costly because of the high accuracy required for the indexing mechanism. Further the perforating rate is low.
Proposals have been made to replace purely reciprocal motion by rotary motion, but these proposals have suffered from the disadvantage that they have incorporated cams to operate the punches and these cause high acceleration rates and consequent high wear and energy requirements. Although in theory such proposed machines can operate at higher output rates than conventional reciprocating machines, the output is not as high as is desirable and the wear factor is against general adoption of such machines.
One of the inherent difficulties in punching holes or recesses in film or in magnetic tape arises because of the difficulty of feeding the tape or film into and out of a rotary machine. This difficulty arises because of the necessity for complete control of the film, particularly during the in-feed operation. Unless there is adequate control the film will not be accurately located in relation to the punches and even a very small deviation is liable to waste large quantities of film.
U.S. Pat. No. 2,760,576 to Spencer issued Aug. 28, 1956, discloses a rotary action film and tape punching or perforating apparatus but such apparatus would not provide the necessary accuracy partly because of the inadequate in-feed and out-feed arrangements and partly because the punches are spring-mounted and this will give rise to inaccuracies resulting from wear and fatigue in the springs even if adequate performance is achieved initially.
Furthermore, it is very important that the film or magnetic tape shall not be scratched or suffer other damage since such damage will produce poor reproduction optically or poor sound reproduction.
Accordingly it is an object of the present invention to provide a rotary film or tape punching machine which can operate continuously for long periods without undue wear of the working parts.
A further object of the invention is to provide a rotary film or tape punching machine which can operate at speeds substantially higher, possibly ten times higher, than conventional reciprocatory machines.
A further object of the invention is to provide a rotary film or tape punching apparatus which will cause substantially no damage to the surface of the film or tape.